The invention described herein relates to the safe storage of either new or spent nuclear reactor fuel assemblies and more particularly to an improved design of spent fuel racks capable of substantially increasing the storage capacity of on-site spent fuel storage pools
The continued delays in establishing and licensing spent nuclear fuel reprocessing facilities has required electric power generating utilities to better utilize their present spent fuel storage pools to maximize the storage of spent fuel assemblies removed from an operating reactor. storage capacity of on-site spent fuel storage pools.
The continued delays in establishing and licensing spent nuclear fuel reprocessing facilities has required electric power generating utilities to better utilize their present spent fuel storage pools to maximize the storage of spent fuel assemblies removed from an operating reactor. To increase the storage density of fuel assemblies, stainless steel containers or cells which house separate fuel assemblies are used to achieve reduction in fuel assembly spacing in the pool. Alternatively, the spacing can be reduced to a further degree by incorporating neutron absorbing substances, such as boron carbide in the cell walls at the time of manufacture, or by attaching neutron absorbing materials to the sides of the cell as separate components. These constructions which permit closer spacing of adjacent fuel assemblies, effectively capture neutrons and keep the fissionable mass in the fuel assemblies from reaching a critical geometry while maintaining the pool temperature at acceptable levels.
Prior designs of spent fuel racks which employ the foregoing constructions to reduce spacing between either new or spent assemblies, often include a network of channel beams connected in a square array to form multiple square openings which receive the containers or cells which house fuel assemblies. The cells are welded to each other or to the channel beams to provide rigidity to the structure and to space adjacent cells designed to receive spent fuel assemblies. A number of fuel assembly cells connected together in this manner form modules which are interconnected and braced to the pool walls thus providing stability against horizontal seismic loadings. Such bracing in conjunction with various types of structural supports at the pool floor interface have resulted in installation difficulties and potential rack displacement from a non-critical design pattern to new positions which may not meet Nuclear Regulatory Commission design criteria for spent fuel pools.
Further since the cells and fuel assemblies are submerged in water, constructions incorporating neutron absorbing substances must utilize materials which are compatible with the pool environment or provide total encapsulation of the material. Some earlier designs of the latter type have experienced swelling of the poison cavities.